In conventional Long Term Evolution (LTE) systems (e.g., LTE Release 10, 11, and 12), Channel State Information Reference Signals (CSI-RSs) are transmitted periodically. FIG. 1 is a diagram showing subframe configurations of LTE Release 12 and 13, respectively. As shown in FIG. 1, in LTE Release 12, the CSI-RS is transmitted periodically (e.g., 5 ms (millisecond) transmission periodicity). On the other hand, in LTE Release 13, the CSI-RS may be transmitted aperiodically (aperiodic CSI-RS). For example, a user equipment (UE) receive the aperiodic CSI-RSs from a base station (BS), it is required that the UE identifies CSI-RS resources used for the aperiodic CSI-RS transmission in subframes from the BS.
However, conventional LTE standards do not support how to reserve CSI-RS resources for aperiodic CSI-RS transmission and how to transmit and receive the aperiodic CSI-RS between the BS and the UE. As a result, the UE may not be capable of identifying the CSI-RS resource for the aperiodic CSI-RS in the subframes transmitted from the BS. Thus, the aperiodic CSI-RS may not be properly performed.